1. Technical Field
This invention relates generally to dynamic oil seals of the type for creating a fluid tight seal between a rotating shaft and a housing.
2. Related Art
Dynamic radial shaft oil seals are designed to have a so-called “oil side” of the seal and an “air side.” These designations pertain to the orientation of the seal when installed, with the oil side facing the interior of the housing in communication with the oil, whereas the air side faces outwardly in exposed relation to the air.
There are at least two different ways in which a radial shaft oil seal can be installed. An “air side installation” is one in which the seal is first installed into the bore of the housing and the shaft (or its wear sleeve) is thereafter installed from the air side axially into the seal assembly (in the direction inward of the housing) to form the annular seal against the seal. An “oil side installation” is the other where the housing and shaft are already present and the seal assembly is slid axially into the housing and simultaneously onto the shaft (or its wear sleeve), such that the shaft enters the seal assembly from the oil side of the seal to form the annular seal. Otherwise, “oil-side” installation requires the seal assembly to be installed into the housing, also referred to as carrier, and then the housing, with seal installed therein, is assembled to an engine over the “all ready in place” shaft such that the shaft passes through the seal from the oil side to form the annular seal.
During installation, regardless of the type of installation method used, the seal must be able to withstand the axial load resulting during installation without causing a seal lip of the seal to reverse fold or otherwise become displaced to a position where the seal lip is ineffective in the fully installed condition. The axial load imparted on the seal lip is largely due to the friction between the seal body/seal lip and an outer surface of the shaft as the two are moved axially relative to one another during installation. Accordingly, it is desirable to minimize the friction generated during installation of the shaft through the seal, however, a delicate balance needs to be maintained in order to attain the desired seal between the seal lip and the shaft. Further, it is important to prevent positive or negative pressures on the oil-side of the seal lip from moving the seal lip out of sealing engagement with the sealing surface, while at the same time, preventing contamination on the air-side from reaching the oil-side of the seal.